What does “was his to take, not theirs” mean

It basically means that whatever the "something" is it belonged to him not someone else. :)

Explanation:

after the signature of the treaty of versailles in june 1919, germany lost nearly 25,000 square miles and a population of 7 million people. these territories included eupen-malmedy area and moresnet which were ceded to belgium. regarding relations with france, germany ceded the sovereignty of the saar coal mines to this country, as well as the provinces of alsace-lorraine.

explanation:

the statement that best explains why the tenth amendment reserves some rights and powers to states is that the framers believed in the principle of federalism. this principle says that some powers are in the hands of a centralized national government, while others are reserved for the governments of several states.